Currently, there is only one manufacturer offering full range of diesel engines, that is Progress Aero Works with Tony Eifflaender. They have 29 and 40 sizes. If select 29 I recommend TBR version. I'm using their engines for a long time without any problems. The largest in my fleet is PAW 35. Otherwise you can search through eBay or similar sites for Enya 30 or Irvine 40 diesels. Enya brothers now produce their engines intermittently and Irvine's are discontinued. However, with any luck you still can find their diesels unused or in good condition. Good luck